A six-month space journey away, Mars often seems an almost impossible planet to reach. But engineers are developing a new engine that could turn six months to six weeks, bringing the Red Planet much, much closer than ever before.

Using the traditional fuel-burning rockets that carried humans on lunar missions, it would take a manned spacecraft six months to travel from the Earth to Mars. While you could find volunteers in spades willing to trade a year in a tin can for a glimpse of another planet, osteoporosis-inducing weightlessness and dangerous radiation render a lengthy trip unfeasible. But attention has turned to ion engines. While a combustion rocket thrusts a space shuttle through the atmosphere, then lets it coast to its destination, ion engines are able to effect a more continuous thrust:

Ion engines, on the other hand, accelerate electrically charged atoms, or ions, through an electric field, thereby pushing the spacecraft in the opposite direction. They provide much less thrust at a given moment than do chemical rockets, which means they can't break free of the Earth's gravity on their own.

But once in space, they can give a continuous push for years, like a steady breeze at the back of a sailboat, accelerating gradually until they're moving faster than chemical rockets.

Engineers at the Ad Astra are seeing promise in VASIMR, an ion engine that uses a radio frequency generator to heat charged particles and create greater thrust than other similar engines. Ad Astra plans to attach a solar-powered VASIMR engine to the International Space Station for tests, and, if they are successful, could use VASIMR periodically to thrust the ISS back into the Earth's orbit.

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But, if the engine were powered by an onboard nuclear reactor, its applications could be much more profound. Using 1000 times the energy of a solar-powered VASIMR, a nuclear-powered VASIMR engine could propel a manned spacecraft to Mars in a mere 39 days. Although the technology to play a nuclear reactor on a space shuttle is still a ways off, many in astrophysics feel the project holds enormous promise. NASA has provided Ad Astra with a small stipend for VASIMR development, and NASA chief Charles Bolden had high praise for the possibility of shortened space travel:

If engines, such as VASIMR, could be developed to take people to the Red Planet in 40 days, "that puts it inside the range of what we feel comfortable of doing with humans," he told New Scientist. "Something like VASIMR – that's a game changer."